Battery charging systems for road vehicles

ABSTRACT

A battery charging system for a road vehicle has a three phase permanent magnet alternator for charging the battery through a full wave rectifier. Thyristors are associated with the full wave rectifier for controlling the supply of power from the alternator to the battery, conduction of the thyristors being determined by a voltage regulator coupled to the battery. The rectifier consists of four thyristors and two diodes, the two diodes being associated with one phase of the alternator and the four thyristors being associated with the other two phases of the alternator. If a voltage surge occurs as a result of the battery being disconnected, then means operate to ensure that gate current is removed from the thyristors to ensure that the thyristors turn off.

United States Patent [191 [451 Jan. 9, 1973 [54] BATTERY CHARGINGSYSTEMS FOR [73] Assignee: Joseph Lucas (industries) Limited,

Birmingham, England 22 Filed: May 18,1971

[21] Appl.No.: 144,578

[30] Foreign Application Priority Data June 13, 1970 GreatBritain.....i....,........"28,745/70 [52] 11.8. CI. ..320/59, 317/33,322/28 [5 1] Int. (11. ..H02p 7/06, H02p 9/30 [58] Field oi Search..320/39, 40, 59, 60, 61; 322/28, 99', 317/33 R, 33 SC, 32

[56] References Cited UNITED STATES PATENTS 3,383,563 5/1968 Wright..3i7/33 SC 3,530,366 9/1970 Schwarm ..322/28 3,571,657 3/1971 Domann..3 17/33 R Primary Examiner-J. D. Miller Assistant Examiner-Robert J.Hickey Attorney-Holman & Stern [57] ABSTRACT A battery charging systemfor a road vehicle has a three phase permanent magnet alternator forcharging the battery through a full wave rectifier. Thyristors areassociated with the full wave rectifier for controlling the supply ofpower from the alternator to the battery, conduction of the thyristorsbeing determined by a voltage regulator coupled to the battery. Therectifier consists of four thyristors and two diodes, the two diodesbeing associated with one phase of the alternator and the fourthyristors being associated with the other two phases of the alternator.if a voltage surge occurs as a result of the battery being disconnected,then means operate to ensure that gate current is removed from thethyristors to ensure that the thyristors turn off.

3 Claims, 2 Drawing Figures BATTERY CHARGING SYSTEMS FOR ROAD VEHICLESThis invention relates to battery charging systems for road vehicles, ofthe kind including a three phase permanent magnet alternator forcharging the battery through a full wave rectifier, thyristorsassociated with the full wave rectifier for controlling the supply ofpower from the alternator to the battery, and a voltage sensitivecontrol circuit controlling the gate current supplied to the thyristorsto regulate the output voltage of the alternator.

The object of the invention is to provide such a system in a form inwhich the risk of damage to components in the system if the batterybecomes disconnected is minimized.

According to the invention, in a battery charging system of the kindspecified the full wave rectifier includes four thyristors and twodiodes, the two diodes being associated with one phase of the alternatorand the four thyristors being associated with the other two phases ofthe alternator, the voltage-sensitive control circuit providing gatecurrent to the four thyristors when the rectifier output voltage isbelow a predetermined value, and removing the gating current when therectifier output voltage is above the predetermined value, the systemfurther including means for sensing a voltage surge caused bydisconnection of the battery, and for ensuring that in thesecircumstances gate current is removed from the thyristors forsufficiently long to ensure that the thyristors turn off.

In one known arrangement, the full wave rectifier consists of threethyristors and three diodes, one thyristor and one diode beingassociated with each phase. In such an arrangement if the batterybecomes disconnected, whilst it is receiving a charging current therewill be a surge between the output lines caused by the inductive energyof the alternator, and this surge will result in the gate current beingremoved from the thyristors. Each thyristor will then turn off as soonas it is reverse biased, so that no further supply is fed from thealternator to the output lines. However, it will be appreciated thatwhether or not a thyristor turns off depends on whether its currentfalls to zero. With such an arrangement each thyristor can conduct byway of one of the diodes associated with the two phases other than thephase with which the thyristor is associated. In some circumstances, thecurrent flow will not fall to zero and so the thyristor will not turnoff, and damage to components in the system can result. A simplesolution to this problem is to provide in the full wave rectifier sixthyristors, but thyristors are expensive, so that this solution is notattractive. The present invention overcomes this problem by using fourthyristors, together with two diodes. Such a system workssatisfactorily, and saves the additional cost of two thyristors providedthat the supply of gate current to the thyristors is not resumed beforethey have all turned off. For this reason, the additional meanssensitive to disconnection of the battery is provided.

In the accompanying drawing,

FIG. 1 is a circuit diagram illustrating one example of the inventionand FIG. 2 is a view similar to FIG. 1 illustrating two modifications ofthe arrangement shown in FIG. 1.

Referring to FIG. 1, a three phase permanent magnet alternator 11supplies power through a full wave rectifier, consisting of fourthyristors 4, 5, 6, 7 and two diodes 8, 9 to a positive supply line 12and a negative supply line 13, which conveniently is earthed. It will beseen that two of the phases of the alternator 11 have two thyristors 4,5 and 6, 7 associated therewith respectively, the third phase beingassociated with the two diodes 8, 9. The battery 14 of the vehicle isconnected between the lines l2, l3 and provides power to a furtherpositive supply line 15 by way of the ignition switch 16 of the vehicle.The ignition-controlled loads (not shown) of the vehicle are connectedbetween the lines 15, 13.

Connected in series between the lines l2, 13 are a pair of resistors 17,18, the junction of which is connected through a Zener diode 19 to thebase of an n-p-n transistor 21 having its emitter connected to the line13 and its collector connected through a resistor 22 to the line 12. Thecollector and base of the transistor 21 are interconnected through aresistor 23, the base of the transistor 21 is connected through aresistor 24 to the line 13, and the collector of the transistor 21 isconnected through a diode 25 to the line 13. The collector of thetransistor 21 is connected to the base of a transistor 26 through theprimary winding 27 of a transformer 30, and a resistor 28 in series withthe winding 27. The emitter of the transistor 26 is connected through aresistor 29 to the line 13, and the collector of the transistor 26 isconnected through a secondary winding 31 of the transformer 30 to theline 15, the winding 31 being bridged by a diode 32 and a resistor 33 inparallel. A capacitor 34 interconnects the lines 15 and 13, and thetransformer includes four further secondary windings 35, 36, 37 and 38.The winding 35 has one end connected to the gate of the thyristor 4through a diode 46 and its other end connected to the cathode of thethyristor 4. The other windings 36, 37, 38 are similarly connected tothe thyristors 5, 6, through diodes 47, 48, 49 respectively. Finallyconnected across the lines 15 and 13, are a pair of resistors 39, 41,the junction of which is connected through a Zener diode 42 and acapacitor 43 in series to the line 13. The junction of the Zener diode42 and the capacitor 43 is connected through a resistor 44 and a diode45 in series to the base of transistor 21.

Assuming for the moment that the output voltage of the battery 14 isbelow the predetermined voltage, then the Zener diodes 19 and 42 arenon-conductive, and hence the transistor 26 and its associated circuitoscillate by virtue of the feedback circuit through the winding 27 andresistor 28. When the transistor 26 is conducting, then since the diode25 is conducting, the transistor 21 is held off by virtue of thenegative voltage at the junction of the resistors 22 and 23. At thisstage, the transformer 30 provides gate current for each of thethyristors 4, 5, 6, 7 so that any forward biased thyristor can turn on.when the transistor 26 is in the non-conducting part of the cycle, thetransistor 21 is turned on by current flowing through the resistors 23and 24, the voltage on the winding 27 reverses, and the current decaysin the winding 31, the diode 32 and the resistor 33.

Each thyristor will turn off again as soon as it is reverse biased, butas long as the oscillator is operating,

pulses are supplied to the gate-cathode circuits of the thyristors at asufficiently high frequency to keep the thyristors conductive, so thatthe thyristors and diodes 8, 9 together constitute a full waverectifier. However, when the battery voltage exceeds a predeterminedvalue, the Zener diode 19 conducts, although the Zener diode 42 does notin normal use conduct even at this stage. When the Zener diode l9conducts, the transistor 21 becomes fully conductive, and the oscillatorceases to operate. No further gate current is now supplied to any of thethyristors, and each thyristors will turn off as soon as it is reversebiased and remain off until the battery voltage falls again, so that theZener diode 19 stops conducting and the transistor 26 starts oscillatingagain.

If a battery lead becomes disconnected so as to interrupt a chargingcurrent, then the voltage between the lines 12 and 13, and the lines 15and 13, will rise rapidly. In these circumstances, the Zener diode 19will of course conduct again, so that the oscillator ceases to operateand no gate current is supplied to the thyristors 4, 5, 6, 7. Since fourthyristors are used in the rectifier, they will inevitably turn offprovided that the gate current is not supplied again before they havetime to do so. It will of course be appreciated that soon after theoscillator ceases to operate the voltage between the lines 12, 13 willfall, and so the Zener diode 19 may cease to conduct before thethyristors have turned off. However, the Zener diode 42 also conductswhen the battery leads become disconnected, it being appreciated thatthe increase in voltage on the lines 12, 13 and of course the line 15,will be far greater in these circumstances than in normal operation ofthe system. When the Zener diode 42 conducts, the capacitor 43 chargesup, the transistor 21 turns on, and the oscillator ceases to operate.However, if the Zener diodes 19 and 42 cease to conduct because thevoltage between the lines 12, 13 and the lines 15, 13 falls below thepredetermined value, then the transistor 21 is still held on by thedischarge of capacitor 43, thereby ensuring that the oscillator does notoperate until the capacitor 43 has discharged. The circuit is designedso that this delay period is sufficient to ensure that the fourthyristors will turn off, preventing indefinite repetition of theover-voltage condition.

The purpose of the resistor 29 is to limit the current through thetransistor'26. The capacitor 34 provides a local return path for highfrequency currents in the transistor 26.

Referring now to the example shown in FIG. 2, the operation is similarto the arrangement shown in FIG. 1, but in this example, an additionalZener diode 51 is connected across the rectified d.c. output in order tolimit the amplitude of the brief surge which occurs upon disconnectionof the battery. The same effect can be achieved by using as the diodes8, 9 Zener diodes which normally operate as ordinary diodes but whichalso are capable of conducting as Zener diodes in order to regulate therectified output voltage. This modification is also shown in FIG. 2, butit is to be appreciated that the use of Zener diodes 8 and 9 is analternative to the use of the Zener diode 51, and that in order to gainthe required advantage there is no need to use both alternatives.

lclaim:

1. A battery charging system including a three phase permanent magnetalternator for charging the battery through a full wave rectifier,thyristors associated with the full wave rectifier for controlling thesupply of power from the alternator to the battery, and a voltagesensitive control circuit controlling the gate current supplied to thethyristor to regulate the output voltage of the alternator, in which thefull wave rectifier includes four thyristors and two diodes, the twodiodes being associated with one phase of the alternator and the fourthyristors being associated with the other two phases of the alternator,the voltage-sensitive control circuit providing gate current to the fourthyristors when the rectifier output voltage is below a predeterminedvalue, and removing the gating current when the rectifier output voltageis above the predetermined value, the system further including delaymeans for sensing a voltage surge caused by disconnection of thebattery, and for ensuring that in these circumstances gate current isremoved from the thyristors for a predetermined period of timesufficiently long to ensure that the thyristors turn off.

2. A system as claimed in claim 1 including a Zener diode connectedacross the output of the rectifier, said Zener diode limiting theamplitude of said surge during said predetermined period of time.

3. A system as claimed in claim 1 in which said diodes are Zener diodes,said Zener diodes limiting the amplitude of said surge during saidpredetermined period of time.

t t i

1. A battery charging system including a three phase permanent magnetalternator for charging the battery through a full wave rectifier,thyristors associated with the full wave rectifier for controlling thesupply of power from the alternator to the battery, and a voltagesensitive control circuit controlling the gate current supplied to thethyristor to regulate the output voltage of the alternator, in which thefull wave rectifier includes four thyristors and two diodes, the twodiodes being associated with one phase of the alternator and the fourthyristors being associAted with the other two phases of the alternator,the voltage-sensitive control circuit providing gate current to the fourthyristors when the rectifier output voltage is below a predeterminedvalue, and removing the gating current when the rectifier output voltageis above the predetermined value, the system further including delaymeans for sensing a voltage surge caused by disconnection of thebattery, and for ensuring that in these circumstances gate current isremoved from the thyristors for a predetermined period of timesufficiently long to ensure that the thyristors turn off.
 2. A system asclaimed in claim 1 including a Zener diode connected across the outputof the rectifier, said Zener diode limiting the amplitude of said surgeduring said predetermined period of time.
 3. A system as claimed inclaim 1 in which said diodes are Zener diodes, said Zener diodeslimiting the amplitude of said surge during said predetermined period oftime.